JPS6086016A - Purification of liquefied carbonic acid - Google Patents

Abstract

PURPOSE:In purifying liquefied carbonic acid containing impurities, to reduce load of a refrigerant to be fed to a CO2 gas cooler and to reduce power of a refrigerator for the refrigerant, by using crude CO2 of raw material as a heat source for evaporation of high-purity liquefied carbonic acid. CONSTITUTION:Liquefied carbonic acid which is cooled and condensed with a refrigerant from the refrigerator 17 by the cooler 12, from which impurities such as O2, N2, CH4, etc. are removed by the impurity removal tank 13 is fed from the return pipe 3 at the top to the CO2 purification column 1, and it is dropped through the filler 10. In the case, liquefied carbonic acid is brough into contact with CO2 gas evaporating from the reservoir part 5 of high-purity liquefied carbonic acid at the bottom of the purification column 1 in the filler 10, the remaining impure gas in the liquefied gas carbonic acid is separated, and the liquefied carbonic acid as high-purity liquefied carbonic acid is put in the reservoir part 5. In order to evaporate high-purity liquefied carbonic acid, a crude CO2 gas containing impurities to be fed to the purification column 1 is introduced from the inlet 7 to the column, liquefied carbonic acid is heated, and the crude CO2 gas itself is cooled, so that load of cooling of the refrigerant to cool the CO2 gas with the refrigerant of the refrigerator 17 by the cooler 12 is reduced, and electrical power for operating the refrigerator is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying liquefied carbonic acid by removing impurities while evaporating it.

Petrochemical off-gas, LPG, LNG, etc. contain carbon dioxide gas that is harmful to combustion, and in order to remove this carbon dioxide gas, the carbon dioxide gas is adsorbed with a solvent to produce a clean, highly pure gas. Although the carbon dioxide gas released from the separated solvent has relatively high purity, it contains several hundred ppm of methane, oxygen, nitrogen, and the like.

Conventionally, this extracted carbon dioxide gas is purified. In this method, carbon dioxide gas is supplied into the purification tower, the carbon dioxide gas in the purification tower is led to a cooler, where it is condensed and non-condensable substances are separated, and then the condensed liquefied carbon dioxide is allowed to fall from the top of the purification tower. On the other hand, a part of the liquefied carbonic acid accumulated at the bottom of the purification tower is evaporated, the falling liquefied carbonic acid and the evaporated carbon dioxide are brought into gas-liquid contact, the impurities dissolved in the liquefied carbonic acid are gasified, and the impurities dissolved in the liquefied carbonic acid are gasified. It is supplied to the cooler together with the carbon dioxide gas in the tower to remove impurities.

Usually, hot oil or high-temperature, high-pressure refrigerant gas from the compressor of a refrigerator is used as the heat source for heating and evaporating the liquefied carbon dioxide accumulated at the bottom of the refining tower. The disadvantage is that the load on the refrigerator increases because heat comes in from other systems, but when using high-temperature, high-pressure refrigerant gas, the load on the refrigerator decreases slightly, but the power cost of the refrigerator can be saved enough. There is a problem that has not yet been resolved.

An object of the present invention is to reduce the load on the refrigerator for condensing carbon dioxide gas in the method for purifying liquefied carbon dioxide gas, thereby saving power.

The present invention utilizes the carbon dioxide gas containing impurities in the purification tower as a heating source for the purification tower, leads it to a cooler to condense it, separates the non-condensed liquid, and then converts the condensed liquefied carbon dioxide into w'fld.
Part of the liquefied carbon dioxide that is supplied to the top of the tower and accumulated at the bottom of the purification tower is evaporated, and the liquefied carbon dioxide that falls down the tower is brought into gas-liquid contact with the evaporated carbon dioxide to dissolve it in the liquefied carbonic acid. In a method for purifying liquefied carbon dioxide, the impurities accumulated in the lower part of the purification tower are gasified and then supplied to the cooler together with the carbon dioxide gas in the tower to remove the impurities. After heating the liquefied carbon dioxide, it is supplied into the ↑ foraging tower, thereby lowering the temperature of the carbon dioxide gas supplied into the tower, and by guiding the carbon dioxide gas to the cooler. This reduces the load on the refrigerator that supplies refrigerant and saves power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments will be described below with reference to the accompanying drawings showing an apparatus for carrying out the method for purifying liquefied carbonic acid according to the present invention.

In the figure, reference numeral 1 denotes a refining column, which has a supply port 2 at the top for supplying crude carbon dioxide gas into the column 1, and above which a return pipe 3 for liquefied carbon dioxide is provided. A carbon dioxide gas outlet 4 is provided at the top. A liquefied carbonic acid reservoir 5 is provided at the bottom of the column 1, and a heat exchanger 6 is provided in the reservoir 5. The lower inlet of the heat exchanger 6 is connected to a crude gas supply source, and the other outlet 8 is connected to the supply port 2 through a supply pipe 9.
It communicates with A packing 10 is provided in the center of the column 1 to bring the flowing down liquefied carbon dioxide into gas-liquid contact with the evaporated and rising carbon dioxide gas.

The outlet 4 at the top of the column 1 is connected via a pipe 11 to a cooler 12, which in turn is connected to an impurity removal tank 13. The lower part of the impurity removal tank 13 is connected to the liquefied carbon dioxide return pipe 3 via a pump 14, and the upper part is connected to an impurity exhaust pipe 15. A pressure regulating valve 16 for regulating the pressure inside the impurity removal tank 12 is connected to the exhaust pipe 15 .

Reference numeral 17 denotes a refrigerator for condensing carbon dioxide gas, which is not shown in the figure, but consists of a compressor and a condenser.The refrigerant leaving the condenser enters the cooler 12 from a pipe 18 via a pressure reducing valve 19.
It is returned to the compressor of the refrigerator 17 through the pipe 20.

In the figure, 21 is a product transfer pipe connected to the liquefied carbonic acid reservoir 5 of the purification tower 1, and 22 is a product transfer pump.

Next, the present invention will be explained in detail.

The lower inlet of the heat exchanger 6 has, for example, a carbon dioxide concentration of 99.
9%, with 1100PP of methane as an impurity.

Contains less than about 100 PPM of oxygen and nitrogen and has a temperature of 4.
Crude gas having a pressure of about 20 kli/d at 0°C is fed into the column 1 from the feed port 2 through the heat exchanger 6. From the outlet 4, the carbon dioxide gas in the tower 1 is led into the cooler 9 via a pipe 11. The refrigerant liquid from the refrigerator 17 is supplied to the cooler 9 after being depressurized by a pressure reducing valve 19. The carbon dioxide passing through the cooler 9 is cooled there, and the condensed liquid is supplied to the impurity removal tank 13. Ru. In the impurity removal tank 13, condensed liquefied carbon dioxide and non-condensable gas such as oxygen are separated, and the condensed liquid is returned to the purification column 1 via the pump 14 and the return pipe 3. Impurities still above the removal tank 13 are exhausted from the exhaust pipe 12. In this case, in the removal tank 13, the condensate from the cooler 12 is slightly flooded, and the pressure regulating valve 16 is applied to the external pressure so that the non-condensed liquid is more easily separated.
is adjusted.

Since methane, oxygen, etc. are not completely separated and are dissolved in the liquefied carbonic acid supplied into the column 1 from the return pipe 3, they flow down into the packing 10 and evaporate from the reservoir 5. Charcoal i
Dissolved impurities are gasified by bringing the gas into gas-liquid contact, and the gas is supplied together with carbon dioxide gas to the cooler 12 to perform the same operation as described above.

Normally, the temperature of the liquefied carbon dioxide in the reservoir 5 is about -19°C, and the temperature of the crude carbon dioxide gas supplied through the heat exchanger 6 is about 40°C.
℃ and in large quantities, it supplies enough heat to evaporate the liquefied carbonic acid in the reservoir 5, and after heat exchange, the refrigerator in the reservoir cooler 12 cools and flows into the tower 1. 17 load will be reduced.

The liquefied carbonic acid after purification is taken out from the product transfer pipe 21 as appropriate, but the product purified as described above has a concentration of liquefied carbonic acid of 99.99%, for example, and impurities include methane, IPPM1 oxygen, etc. is 4 PPM, nitrogen is 1
A product of extremely high purity containing about 5 ppm can be obtained and can be used as a raw material for carbonated drinks, dry ice, etc.

As is clear from the above detailed description, the present invention exhibits the following excellent effects.

(1) Since carbon dioxide gas containing impurities is supplied into the tower after exchanging heat with liquefied carbon dioxide sprinkled at the bottom of the purification tower, the load on the refrigerator that is cooled by the cooler can be reduced. Power can be saved.

(2) The crude gas is supplied to the heat exchanger 5, and the heat is used to evaporate the liquefied carbonic acid, so it is not the heat of conventional hot oil.

This eliminates the need for a power supply and the time and effort required for piping.

[Brief explanation of the drawing]

The accompanying drawing is a diagram showing an example of an apparatus for carrying out the method for purifying liquefied carbonic acid according to the present invention. In the figure, 1 is the purification tower, 2 is the carbon dioxide gas supply port, and 3 is the return pipe.
is a liquefied carbonic acid reservoir, 6 is a heat exchanger, 12 is a cooler, 1
3 is an impurity removal tank, 17 is a refrigerator, and 19 is a pressure reducing valve. Patent Applicant: Nobuo Kinutani, Patent Attorney, Ishikawajima-Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] Carbon dioxide gas containing impurities is supplied into the purification tower, the carbon dioxide gas in the purification tower is led to a cooler and condensed, non-condensables are separated, and the condensed liquefied carbon dioxide is sent to the upper part of the purification tower. In a method for purifying liquefied carbon dioxide, in which the liquefied carbon dioxide accumulated in the lower part of the purification tower is partially evaporated and brought into gas-liquid contact with the falling liquefied carbon dioxide, the carbon dioxide gas supplied into the purification tower is supplied to the lower part of the tower. A method for purifying liquefied carbonic acid, which comprises supplying the liquefied carbonate into a column after exchanging heat with the liquefied carbonic acid accumulated in the column.